De Leon Vanegas Jr. was sentenced Wednesday to 18 years in prison for giving "cheese" heroin to his girlfriend's brother. Fernando Cortez Jr., 15, died hours after snorting the illegal drug last spring.

Mr. Vanegas, 20, must serve half of the sentence before he is eligible for parole. Prosecutors believe Mr. Vanegas is the first person in North Texas convicted of causing a death by giving someone cheese heroin.

Bianca Cortez, now the ex-girlfriend of Mr. Vanegas, testified for the prosecution during the two-day trial. As Criminal District Judge Robert Burns read the jury's sentence Wednesday afternoon, Bianca fought back tears.

"I feel like 18 years is too much," said Bianca, 17. "I'm not saying anyone should feel sorry for De Leon. But my brother was old enough. He knew how to say, 'Yes' and 'No.' "